Welcome back but that is long time gone.
Except from very rare edge cases, new players do not belong to PvP. Sorting such rushers out is a good way to prevent the common PvP frustration they get instantly, facing veteran PvP factions on the server.
However, if some really want PvP they can get PvP - with and without Magnesium.
Magnesium can be found in PvE: here.
Magnesium can be found in some special locations.
Can be found in PDA and EGS HQ Missions (PvPvE)
And can be bought on ECC for relative cheap at the NPC Trader.
Because other servers don’t give a heck about PvP in the first place. But that is off-topic.
I explained it already above.